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lightfast

[lahyt-fast, -fahst]
adjective
  1. not affected or faded by light, especially sunlight; colorfast when exposed to light.
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Origin of lightfast

First recorded in 1955–60; light1 + fast1
Related formslight·fast·ness, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for light-fast

light-fast

adjective
  1. (of a dye or dyed article) unaffected by light
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012